Re: DCC Distribution comments, please


Blair & Rasa
 

Allan
See individual responses below. By the way, thank you both for the effort
put into your website, which I've been following for at least two years now,
and for this new group. Just pulling this together so I could ask some
questions has served to both focus my thinking on the bus issues, and
address some misgivings I had.

Regarding PS2012: I prefer to have a power source with each
booster/command station. Given the cost of individual power sources
and the PS2012, there really isn't a cost advantage either way. The
PS20212 surprises me as a product because I thought Digitrax was one
of the manufacturers that advised against using a common power source
for their boosters.
They've said in their manual that this is because each booster should have
it's own current protection device, which seems to be why they also include
a Y-adapter (including current limiters) to feed multiple boosters from the
PS2012. Anyway, I'm in your camp for other reasons; home-kitting
half-a-dozen 5-Amp boxes with transformers, fuzes, switches, idiot lights,
and suitable connection means is a no-brainer, and then I know what I've
got, and it's modular; not to mention ease of repair.

Note that the Digitrax command station and
boosters can be powered by AC sources. DC is not required.
yep. And transformers are cheap. I've never seen a schematic for a DCC
booster, but I presume the first input element is a bridge rectifier (this
permits use of either polarity of DC as well as AC for feed - maximizes
robustness); if so, putting a bridge in the transformer chassis would be
redundant unless the transformer chosen is high enough in voltage that we
want to shed a few watts OUTSIDE the booster. BUT, do boosters run cooler
with DC rather than AC input? Does anyone know? It doesn't seem reasonable
from a transformer-diode-filter cap type of power supply point of view, but
I presume they're using switching technology given the size of the box for a
DCS100, so I don't know if there are differences in efficiency between
sinusoid AC and smooth DC input.

Loconet plugs: The only reason to have more Loconet plugs is if
someone comes over to operate that doesn't have wireless capability.
Okay, hadn't considered that, but it's my layout. If I'm willing to
relegate visitors to yard ops unless they bring a radio throttle, that's my
choice.

Loconet: There is no practical restriction as to how long your
Loconet can be. You can run it anywhere, anyway you want to.
Feeder length: Feeder lengths of 24" is not advised, but if you can
pass the short test (see http://www.wiringfordcc.com/track.htm#a16)
you can do it. You might want to consider branching off your main bus
with more 14 AWG sub buses to get shorter feeder lengths.
Okay, theory discussion follows. Is it better to put a joint in the
high-current main bus, or a bit more length in the
feeders? Thinking about it, the resistance of a copper-solder-copper joint
has just got to be up there in the same league as several feet of smaller
gauge wire. So unless I'm off-base, and I haven't actually checked this
with the a milli-ohmmeter, it would actually not really matter which way I
went. The primary concern is the coin test, and that's up to me to try. As
far as I'm concerned, any branch in the main bus is at least as much of
concern as multiple feeders, because the main bus joint will see a larger
proportion of the total current being delivered to the loads.

Blair Smith
Deep River, Ontario, Canada.
Where there's still 18" of snow in the bush, and a good month for model
railroading before the yardwork begins.

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